Comparison of two rotor temperature estimation models of a surface cooled squirrel cage induction machine

Stator and rotor temperature of a motor drive are important quantities with respect to the utilization and the overload capability. Permanent thermal stress and disregard of the temperature class specification may cause insulation deterioration with subsequent failure as well as rotor faults. Since the on-line measurement of rotor temperature is very difficult and expensive, estimation techniques are preferred. In this paper two rotor temperature estimation techniques are compared. The first technique basically determines the rotor resistance by means of comparing state variables of two different machine models. The second model evaluates a complex thermal equivalent circuit including thermal resistances and capacitances. The results of these models are also compared with some measuring data obtained from a four pole 18.5 kW motor